The proposed research has two aims: The first is to use neuronal recordings in awake behaving rhesus monkeys to test models of rapid two-choice decision making that have been derived from data from human subjects. The models have been applied to simple perceptual tasks in which humans are asked to decide which of two stimuli was displayed, and they provide a good description of the speed and accuracy characteristics of the data. Monkeys can be trained to perform the same perceptual tasks with relative ease, using eye movements to one of two targets to indicate their decisions instead of the key presses used by humans.
Our aim i s to investigate whether the components of processing identified by cognitive models are reflected in neural activities.
The second aim of the research is to investigate the joint behavior of small subsets of the neuronal populations that decide the direction, distance, and timing of eye movements. We plan to use simultaneous recordings from up to six neurons to examine correlations in the activities of neurons of different types and locations. Central questions are whether neurons hypothesized to perform the same function exhibit the same patterns of firing, whether neurons in the different parts of the oculomotor system show synchronous activities, whether the neurons responsible for movement to one of the possible choices interact with the neurons responsible for movement to the other choice, and how changes in stimulus information in the course of a single trial affect neuronal firing rates. The two aims of the research are tightly intertwined in that hypotheses and results from one of the domains will inform choices of hypotheses in the other. The primary oculomotor system is ideal for examining the neural decision processes that precede the generation of eye movements. We propose to investigate the possibility that neurons in the frontal eye field and superior colliculus that show preparatory and saccade-related burst activities prior to eye movements map onto the components of the diffusion model. To put it naively, wouldn't it be amazing if this neural activity was well-described by the characteristics of the accumulation of information reaching a threshold in the diffusion model? With this possibility in mind, the beginning phases of the proposed research will use the diffusion model to guide the designs of experiments with monkeys, to provide estimates of component processes through model fits to the behavioral data, and to guide the analysis of neural data. These experiments will make direct comparisons between human and monkey decision-making systems. Because of known and expected similarities between rhesus monkey and human oculomotor systems, these experiments will also provide a model for the functional organization of the neural control of voluntary movement in humans.
| Ratcliff, Roger; Hasegawa, Yukako T; Hasegawa, Ryohei P et al. (2011) Inhibition in superior colliculus neurons in a brightness discrimination task? Neural Comput 23:1790-820 |
| Starns, Jeffrey J; Ratcliff, Roger (2010) The effects of aging on the speed-accuracy compromise: Boundary optimality in the diffusion model. Psychol Aging 25:377-90 |
| Ratcliff, Roger; Hasegawa, Yukako T; Hasegawa, Ryohei P et al. (2007) Dual diffusion model for single-cell recording data from the superior colliculus in a brightness-discrimination task. J Neurophysiol 97:1756-74 |
| Farrell, Simon; Ratcliff, Roger; Cherian, Anil et al. (2006) Modeling unidimensional categorization in monkeys. Learn Behav 34:86-101 |
| Ratcliff, Roger; Cherian, Anil; Segraves, Mark (2003) A comparison of macaque behavior and superior colliculus neuronal activity to predictions from models of two-choice decisions. J Neurophysiol 90:1392-407 |
